<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 200px;
            background-color: lightblue;
            /* border-radius: 0; */
            /* transition: 过渡属性值 过渡时间 运动速度曲线 延迟时间; */
            /* 过渡动画触发的条件，当这个过渡属性发生变化时，才会触发 */
            /* transition: border-radius 2s ease 1s; */
            transition: width 2s;
        }

        .box:hover {
            /* border-radius: 50%; */

            width: 400px;
        }
    </style>
</head>
<body>
    <div class="box"></div>
</body>
</html>